Semiconductor light emitting devices, such as a light emitting diode (LED), may be provided in a package for protection, color selection, focusing, and the like for light emitted by the device. An LED package generally includes a substrate member on which an LED is mounted. The LED may include a mounting pad attached to the substrate member with electrical connections being made to the LED for applying an electrical bias. LEDs generally comprise an active region of semiconductor material sandwiched between two oppositely doped layers. When a bias is applied across the doped layers, holes and electrons are injected into the active region where they recombine to generate light. Light is emitted omnidirectionally from the active layer and from all surfaces of the LED. The substrate member may also include traces or metal leads for connecting the package to external circuitry and the substrate may also act as a heat sink to conduct heat away from the LED during operation.
An LED package may include a lens positioned for receiving light emitted by an LED in the package. The lens may include optical materials intended to influence or change the nature of the light emitted by the LED. Further, the lens may be suitably shaped for scattering the light and/or otherwise redirecting or influencing the light.
Increasingly, LED packages are finding their way into everyday commercial products such as flashlights, spotlights, safety vehicle lighting, and internal vehicle lighting systems. For various reasons, devices providing a range of light beam colors are sought by military personnel, law enforcement personnel, and hunters. For example, red light can be used on vessels and helicopters at night so as not to disturb night vision of the human eye while still allowing maneuverability. Also, blue light can be used to differentiate and follow certain liquids (e.g., blood, oil, hydraulic fluid, etc.) since particular liquids absorb blue light wavelengths differently. This can be advantageous for hunters tracking animal blood when visibility is limited or automotive technicians seeking the source of an oil leak.
LED packages provide a challenge in effecting the different color beams needed for these various applications. In current lighting units, beam filters are mechanically attached and employed to filter white light for providing the various color beams. The beam filters can be either added to the light in front of a lens as a mechanical attachment or by some other design intent. Typically, as described in U.S. Pat. No. 6,761,467 to Matthews et al., the beam filters operate on a flip-up design that allows a quick transition back to a white light beam. In other aspects, the beam filters operate by rotating the lens in front of the light source, which is offset from the central body axis, to allow selection of multiple beam filters by rotation of the lens.
Additionally, multiple color lamps can be positioned inside lighting units such as flashlights to provide various color beams. These lighting units change colors, however, by activating individual lamps wherein each individual lamp comprises a single chip emitting a single color. This configuration of multiple lamps does not approach the brightness needs or reflector efficiency required for these lighting units. Also, the use of multiple lamps is limited by size constraints of the lighting unit such that the lamps are off-centered, leading to beam shifting. It is therefore desirable to provide improvements in LED lighting units capable of emitting multiple color light beams. Particularly, it would be beneficial to eliminate the use of beam filters and multiple lamps within the lighting unit housing.
Accordingly, there exists a long-felt need for LED multi-chip lighting units and related methods that provide improvements in lighting units employing various color light beams as well as the powering properties afforded by LEDs versus traditional gas filled lighting sources.